Online tools for filling information needs are becoming increasingly sophisticated. As these tools have evolved, the relevance of discovered information, e.g., search results, have improved while the requirements of users in terms of adhering to syntactical rules (e.g., use of Boolean operators) continue to decrease. Some tools are now capable of interpreting and responding to natural language input. However, these tools generally operate according to a simple query-response model in which a user formulates a query and the tool responds, with the response being determined solely by the user's query. Given the inherent variability and ambiguity of natural language, this model can lead to a frustrating user experience when the tool cannot understand the user's input and/or does not have sufficient information to generate a useful response.